Vettel, bidding for a fifth consecutive title, comes into Sunday's race at Albert Park with his team scrambling to come to grips with the new hybrid turbo era in Formula One.
Red Bull, one of four teams using the troubled Renault power unit, was unable to finish a race simulation for either Vettel or his new Australian team-mate Daniel Ricciardo, and badly lagged rivals Mercedes and Ferrari in terms of mileage.
"It will be a very different car," the 26-year-old told reporters at Albert Park.
"Obviously, we had a lot of problems during the tests, we didn't get to test a lot of stuff and we hope to do some more running here."
Red Bull's struggles to adapt to the new V6 engine have given rival teams hope of ending their four-year stranglehold on the constructors' and drivers' championships, or at a minimum end the German's run of nine consecutive race victories.
Vettel, who has not lost a race since July, said little to lift the gloom hanging over his team's garage, but was adamant that just finishing the race was not the limit of Red Bull's ambitions in Melbourne.
"We know that we are not in the best shape yet. There are a lot of things we need to sort," said Vettel, a 2011 winner at Albert Park and third last year.
"Unfortunately, you can't solve all of them overnight. We'd love to but we cant. We really have to go step-by-step together with Daniel.
"It's no secret you need very, very strong reliability to be a title contender.
"I'm going out of here not trying to just make it round, I'm going round here to push to the maximum and do the best I can, and then we'll see where we are and how far we get.
"The target, for sure, is to finish, and the target for sure is to finish in the best possible position. That's the mindset, it's fairly straightforward.
"We have a strong team, good people on board ... I'm confident we should progress as the season goes on."
After an occasionally tempestuous five years with the plain-spoken Mark Webber, Vettel has a younger Australian team mate in the garage in Ricciardo, who graduated from sister team Toro Rosso.
Vettel joked that he had little advice to give the 24-year-old after pre-season testing.
"Not much, we didn't drive that much this year, so there's not much I could talk about," he said.
"Obviously you do your own thing once you're in the car."
Having battled manfully through countless media appearances in the leadup to his home grand prix, Ricciardo will face a huge task holding his own against his more senior team mate out on the track.
"For now, (I'll) just focus on what I've done for the last few years," he said. "Just keep doing what I've been doing to get to this point and then see how it's feeling.
"Obviously I get a good view behind the scenes with the engineers, and also with how Seb works with his guys and understand a bit more through that but for now it's just do my thing and see where I stand."
- Sports & Recreation
- Motor Racing
- Red Bull
- Daniel Ricciardo